1. Field of the Invention
This invention relates to a distributed database system and its data retrieval methods. In more detail, the invention relates to a system in which multiple terminals, each having distributed databases, are connected to a public network.
2. State of the Prior Art
FIG. 16 shows an example of the configuration of a distributed database system. Terminals 6, 7 and 8 are connected to a public network 5. Respective databases 6a, 7a and 8a are provided in terminals 6, 7, and 8 having contents designated 6b, 7b, and 8b.
The terminals 6, 7, and 8 contain the respective databases 6a, 7a, and 8a, and manage the respective contents 6b, 7b, and 8b. Upon receipt of a data retrieval request, the terminals 6, 7, and 8 locate the terminal managing the data using the appropriate contents. The terminals 6, 7 and 8 then access the terminal via the public network 5, and request data to be retrieved.
The following explains in detail the case where data retrieved is displayed.
In the distributed database, data processing is performed by carrying on a dialogue with a display screen at a terminal, such as a workstation. The terminal retrieves the screen needed for displaying. The display screen must be retrieved quickly in order to perform data processing efficiently.
To retrieve a display screen registered in the terminal, a keyword assigned to the display screen name is specified. The terminal has a keyword table managing one or more keywords assigned to each display screen name, as shown in FIG. 17. When a keyword is specified by a user, the terminal displays the name of the display screen to which the specified keyword is assigned. This is done according to the keyword table. Note that when more than one display screen is available, a list is displayed. A display screen is retrieved in this manner.
Keyword information assigned to the display screen of each terminal is not managed according to the concept of distributed processing.
However, when a keyword is specified, one terminal must search for that keyword. The search begins with the first display screen name of the keyword table and lists display screen names to which the specified keyword is assigned. Namely, the entire keyword table must be searched. A substantial amount of time is required to retrieve display screens. Retrieval time increases in proportion to the number of display screens registered.
In addition, since keyword information assigned to display screens of each terminal is not managed in a distributed manner, retrieval of display screens must be performed in each terminal according to the keyword. Therefore, the display screen of terminals in identical distributed database systems cannot be easily retrieved.
Furthermore, since stand-alone terminals are heavily loaded by the data retrieval described above, processing specific to the terminals may not be performed.